Hierarchical indicies

1. A computer program product comprising a machine-readable medium storing instructions that, when executed by at least one programmable processor, cause the at least one programmable processor to perform operations comprising: storing, in a plurality of main part fragments, a plurality of data records that comprise a data set, each main part fragment comprising a subset of the set of data records; assigning a relative age to each main part fragment of the plurality of main part fragments; creating, for a newest of the main part fragments, a fragment-specific index segment, the fragment-specific index segment providing a lookup ability for logical identifiers of data records in just the newest of the main part fragments; and providing, for two or more older main fragments, a multi-fragment index segment that spans the two or more older main fragments, the multi-fragment index segment providing a lookup ability for logical identifiers of data records in the two or more older main part fragments.

2. The computer program product as in claim 1 , wherein at least one of the two or more older main fragments is a closed main fragment.

3. The computer program product as in claim 2 , wherein operations further comprise: reorganizing the closed main fragment; and updating the multi-fragment index segment in response to the reorganizing.

4. The computer program product as in claim 3 , wherein the operations further comprise: updating row indices in leaf nodes of the multi-fragment index segment to point to new row indices after the reorganizing.

5. The computer program product as in claim 1 , wherein the logical identifiers comprise globally unique RowID values for each data record in each main part fragment.

6. The computer program product as in claim 1 , wherein the operations further comprise providing for three or more additional main fragments, an additional multi-fragment index segment that spans the three or more additional main fragments, the additional multi-fragment index segment providing a lookup ability for logical identifiers of data records in the three or more additional main part fragments, the three or more additional main part fragments being older than the two or more older main fragments.

7. A system comprising: at least one programmable processor; and a machine-readable medium storing instructions that, when executed by at least one programmable processor, cause the at least one programmable processor to perform operations comprising: storing, in a plurality of main part fragments, a plurality of data records that comprise a data set, each main part fragment comprising a subset of the set of data records; assigning a relative age to each main part fragment of the plurality of main part fragments; creating, for a newest of the main part fragments, a fragment-specific index segment, the fragment-specific index segment providing a lookup ability for logical identifiers of data records in just the newest of the main part fragments; and providing, for two or more older main fragments, a multi-fragment index segment that spans the two or more older main fragments, the multi-fragment index segment providing a lookup ability for logical identifiers of data records in the two or more older main part fragments.

8. The system as in claim 7 , wherein at least one of the two or more older main fragments is a closed main fragment.

9. The system as in claim 8 , wherein operations further comprise: reorganizing the closed main fragment; and updating the multi-fragment index segment in response to the reorganizing.

10. The system as in claim 9 , wherein the operations further comprise: updating row indices in leaf nodes of the multi-fragment index segment to point to new row indices after the reorganizing.

11. The system as in claim 7 , wherein the logical identifiers comprise globally unique RowID values for each data record in each main part fragment.

12. The system as in claim 7 , wherein the operations further comprise providing for three or more additional main fragments, an additional multi-fragment index segment that spans the three or more additional main fragments, the additional multi-fragment index segment providing a lookup ability for logical identifiers of data records in the three or more additional main part fragments, the three or more additional main part fragments being older than the two or more older main fragments.

13. computer-implemented method comprising: storing, in a plurality of main part fragments, a plurality of data records that comprise a data set, each main part fragment comprising a subset of the set of data records; assigning a relative age to each main part fragment of the plurality of main part fragments; creating, for a newest of the main part fragments, a fragment-specific index segment, the fragment-specific index segment providing a lookup ability for logical identifiers of data records in just the newest of the main part fragments; and providing, for two or more older main fragments, a multi-fragment index segment that spans the two or more older main fragments, the multi-fragment index segment providing a lookup ability for logical identifiers of data records in the two or more older main part fragments.

14. The computer-implemented method as in claim 13 , wherein at least one of the two or more older main fragments is a closed main fragment.

15. The computer-implemented method as in claim 14 , further comprising: reorganizing the closed main fragment; and updating the multi-fragment index segment in response to the reorganizing.

16. The computer-implemented method as in claim 15 , further comprising: updating row indices in leaf nodes of the multi-fragment index segment to point to new row indices after the reorganizing.

17. The computer-implemented method as in claim 13 , wherein the logical identifiers comprise globally unique RowID values for each data record in each main part fragment.

18. The computer-implemented method as in claim 13 , further comprising: providing for three or more additional main fragments, an additional multi-fragment index segment that spans the three or more additional main fragments, the additional multi-fragment index segment providing a lookup ability for logical identifiers of data records in the three or more additional main part fragments, the three or more additional main part fragments being older than the two or more older main fragments.

19. The computer-implemented method as in claim 13 , wherein at least one of the storing, the assigning, the creating, and the providing is performed by a system comprising one or more programmable processors.